1. Field of the Invention
This invention relates to polymeric compounds having one or more hydroxyl and/or carboxyl groups in the molecule wherein part or all of the hydrogen atoms of the hydroxyl and/or carboxyl groups are replaced by groups of the general formula (1) that will be given later and which, when used as base resins in resist materials, can yield chemically amplified positive type resist materials exhibiting very high alkali dissolution contrast before and after exposure to light, having high sensitivity and high resolution, and hence especially suitable for use as fine pattern-forming materials in the fabrication of very large scale integrated circuits, and to chemically amplified positive type resist materials containing such polymeric compounds, and to a process for pattern formation.
2. Description of the Related Art
In recent years, a finer pattern design rule has come to be desired with an increase in the integration density and operating speed of large scale integrated circuits. Under these circumstances, deep ultraviolet lithography is regarded as a promising fine patterning technique of the next generation. Deep ultraviolet lithography permits patterning even to a size of 0.5 .mu.m or less and, when a resist material having low light absorptivity is used, enables the formation of patterns having sidewalls almost perpendicular to the substrate.
Recently developed chemically amplified positive type resist materials using acid catalysts (as described in Japanese Patent Publication (JP-B) No.2-27660/'90, Japanese Patent Provisional Publication (JP-A) No. 63-27829/'88) are expected to be especially promising resist materials for deep ultraviolet lithography which utilizes a KrF excimer laser having high luminance as a light source of far ultraviolet radiation and is characterized by high sensitivity, high resolution and good resistance to dry etching.
As such chemically amplified positive type resist materials, two-component systems comprising a base resin and an photo-acid generator and three-component systems comprising a base resin, an acid generator and a dissolution inhibitor having acid-labile groups are known.
For example, a resist material comprising poly-p-tert-butoxystyrene and an acid generator is proposed in Japanese Patent Provisional Publication No. 62-115440/'87. Moreover, as resist materials analogous thereto, a two-component resist material comprising a resin having tert-butoxy groups in the molecule and an acid generator is proposed in Japanese Patent Provisional Publication No. 3-223858/'91, and a two-component resist material comprising polyhydroxystyrene containing methyl, isopropyl, tert-butyl, tetrahydropyranyl and trimethylsilyl groups and an acid generator is proposed in Japanese Patent Provisional Publication No. 4-211258/'92.
Furthermore, a resist material comprising a polydihydroxystyrene derivative, such as poly[3,4-bis(2-tetrahydropyranyloxy)styrene], poly[3,4-bis(tert-butoxycarbonyloxy)styrene] or poly[3,5-bis(2-tetrahydropyranyloxy)styrene], and an acid generator is proposed in Japanese Patent Provisional Publication No. 6-100488/'94.
However, the base resins used in these resist materials have acid-labile groups in side chains. Thus, if the acid-labile groups are ones capable of being decomposed by a strong acid (i.e., tert-butyl and tert-butoxycarbonyl groups), they may be deactivated as a result of reaction with basic compounds present in the air. Consequently, the acid-labile groups become difficult to decompose, so that the patterns of the resist material tend to form a T-top profile. On the other hand, alkoxyalkyl groups such as ethoxyethyl are decomposed by a weak acid and, therefore, are not significantly affected by basic compounds present in the air. However, when polymers having bulky groups or a high degree of substitution are used in order to achieve a high dissolution-retarding effect on alkali, they involve problems such as low thermal resistance and insufficient sensitivity and resolution. Thus, these resist materials are still less than satisfactory for practical purposes. Accordingly, it would be desirable to solve these problems.